Acoustics technology, and in particular stereo technology, has advanced to meet the demand for improved sound quality. The rising popularity in home theater systems and related sound technologies has refocused the stereo industry towards improved and more efficient sound systems. Sound systems are also an integral part of vehicles of all types. Advances in acoustics and electronics technology have resulted in smaller and more efficient delivery systems. Nevertheless, acoustic principles demand relatively lengthy transmission lines or acoustic paths. For example, known acoustic paths may extend up to several feet. Space restrictions in houses, vehicles, and mobile stereos, however, limit the use of such acoustic paths and the relatively large enclosures that house them.
Production of sound within an enclosure, whereby acoustic waves are directed along an acoustic path, is a critical aspect of the process. Specifically, sound is produced by an acoustic source, for example, a driver, and then directed along an acoustic path to an opening. The shape of the acoustic path affects the quality of sound exiting the outlet.
Existing apparatus address the problem of improving sound quality while minimizing space requirements by incorporating acoustic paths having sharp bends (i.e., folded paths) such that the acoustic path fits within the enclosure. The folded or labyrinth designs for acoustic paths require sharp bends that disrupt airflow, and thus degrade sound quality and increase mechanical noise. Further, known devices incorporate relatively long acoustic paths that are unsuitable for use in close quarters (e.g., apartments and car stereos).
Known apparatus also address the problem of minimizing space requirements by incorporating helical acoustic paths, wherein structures housed within the enclosure define a single helix acoustic path. The single helix design, however, fails to recognize the benefits of a double helix structure. Specifically, the single helix design limits the air mass (i.e., acoustic mass) that provides the medium for transmitting the acoustic waves.
For example, U.S. Pat. No. 5,824,969 (the '969 patent) and U.S. Pat. No. 6,078,676 (the '676 patent) to Takenaka disclose a speaker system having a single spiral sound passage. Both Takenaka patents disclose a lower T-joint for supporting an outer tube, an inner tube for supporting a partition plate arranged in a spiral pattern, an upper T-joint connected to the top end of the outer tube, and a speaker unit secured to the upper T-joint. As described, the Takenaka patents rely on a single passage for directing sound radiating from the rear of the speaker. Specifically, the Takenaka patents incorporate a single inlet opening leading into a single passage that is in communication with a single outlet opening. Although both patents address the problem of sharp or acute bends in the sound passage, the '969 and '676 patents fail to recognize the advantages of incorporating two sound passages in the shape of a double helix. Further, the Takenaka patents describe the use of a dual tube structure wherein the inner tube supports the partition plate. Thus, Takenaka further restricts the limited area of the single sound passage—and thus total medium (i.e., air) for transmitting sound—by incorporating a support structure for the spiral plate. Thus there exists a need for an apparatus that maximizes the total area of the sound passage without adversely affecting the overall size of the enclosure housing the acoustic source and acoustic guide.
Still other known apparatus incorporate double helix channels into an enclosure, yet position the channels around the periphery of the driver and around an inner sleeve that supports the driver at a front end. In this configuration, inlets for directing sound into the channels are adjacent the rear end of the inner sleeve and outlets of the passage are adjacent the front of the driver. This design, wherein the radius of the acoustic channel is a fraction of the total radius of the enclosure or inner sleeve, recognizes the need to maximize space, yet sacrifices sound quality by directing the sound from the driver in opposing directions (i.e., front to rear and then rear to front). The relatively small channels tend to create mechanical resonance, increase harmonic distortion, and restrict low frequency reproduction.
For example, U.S. Pat. No. 6,062,339 to Hathaway describes an enclosure for housing a loudspeaker. Specifically, Hathaway discloses an outer sleeve that supports and surrounds an inner sleeve, a loudspeaker connected to a front end of the inner sleeve, and an insert positioned between the outer sleeve and inner sleeve. The insert defines two spiral channels that surround the inner sleeve. The channels direct sound advancing from the rear of the front-mounted speaker, around the inner sleeve (i.e., between the inner and outer sleeve), and out of the front of the enclosure. Hathaway relies upon two spiral channels that wind around the outer surface of the inner sleeve that supports the loudspeaker. Thus, the sound must travel in opposing directions before exiting the enclosure. Specifically, the sound must travel rearward the length of the inner sleeve, and then forward through the channels between the inner and outer sleeve. Thus, Hathaway fails to recognize the benefits of a pair of acoustic paths having the shape of a double helix that effectively doubles the volume of air (i.e., medium) for transmitting the sound. Stated differently, Hathaway recognizes the need to maximize space by wrapping the channels around the inner sleeve, yet sacrifices sound quality by directing the sound from the driver in opposing directions (i.e., front to rear and then rear to front). Accordingly, Hathaway fails to address the problem of maximizing the radius—and thus the total area—of the channels. Unfortunately, the structure of Hathaway creates mechanical resonance, increase harmonic distortion, and restrict low frequency reproduction.
Accordingly, there exists a need for an apparatus for improving the quality of sound from an acoustic source housed within an enclosure that directs sound in one direction in such a manner to dampen mechanical resonance, reduces harmonic distortion, and extends low frequency reproduction.
Known devices also include six or more resonant antinodes along the acoustic path that cause impedance variations at specific frequencies, and therefore creates uneven amplitude response. One option to counteract the uneven amplitude response is to incorporate damping material into the inlets of the acoustic paths. However, the addition of damping material into the inlets reduces the efficiency of the system, and therefore is a less desirable option. Moreover, the amount of damping material is dictated by the amount of available free space in the enclosure and acoustic path. Thus, a need exists for an enclosure and acoustic guide that does not require damping material to lessen uneven amplitude response.
A more attractive option in addressing the failures above is to increase the total area of the acoustic path without increasing the total size of the enclosure and without enhancing mechanical resonance, increasing harmonic distortion, or restricting low frequency reproduction. In this fashion, sound quality of the apparatus is not sacrificed for smaller sizes.